Use este script para remover automaticamente o ppas inexistente, causando erro 404.
#!/bin/bash
sudo rm /tmp/update.txt; tput setaf 6; echo "Initializing.. Please Wait"
sudo apt-get update >> /tmp/update.txt 2>&1; awk '( /W:/ && /launchpad/ && /404/ ) { print substr($5,26) }' /tmp/update.txt > /tmp/awk.txt; awk -F '/' '{ print $1"/"$2 }' /tmp/awk.txt > /tmp/awk1.txt; sort -u /tmp/awk1.txt > /tmp/awk2.txt
tput sgr0
if [ -s /tmp/awk2.txt ]
then
tput setaf 1
printf "PPA's going to be removed\n%s\n" "$(cat /tmp/awk2.txt)"
tput sgr0
while read -r line; do echo "sudo add-apt-repository -r ppa:$line"; done < /tmp/awk2.txt > out
bash out
else
tput setaf 1
echo "No PPA's to be removed"
tput sgr0
fi
Copie e cole em um arquivo de texto, torne este executável executando chmod +x filename
e execute ./filename